The present invention relates to a process for the production of a precipitated silica.
Synthetically produced silicas have for many years played an important role as a constituent of dental care products. A range of processes for the production of silicas specially tailored for use in toothpastes is known. These processes are associated with processing disadvantages making them both economically and ecologically unsatisfactory.
In one type of process, large quantities of electrolytes are used which must subsequently be washed out again in order to achieve the necessary purity of the end product. This brings about a considerable salt loading of effluents (U.S. Pat. Nos 3,960,586 and 4,122,161 which are incorporated by reference in their entirety; DE-AS 24 46 038). Other processes incorporate additional partial stages to prepare particular initial precipitation mixtures or additional hydrothermal reaction stages with several isolation stages (U.S. Pat. No. 5,286,478 which is incorporated by reference in its entirety; EP-B 0 317 378).
A process for the production of a reinforcing precipitated silica with a surface area of above 200 m.sup.2 /g is known from DE-B 14 67 019. This precipitated silica is not suitable for use in toothpastes.
A further disadvantage of known processes is the low space-time yield during precipitation due to the necessary introduction of a stop interval (ageing stage) or by the use of dilute reaction components. In this manner, solids contents of only approximately 40-60 g SiO.sub.2 /l are customarily obtained on completion of precipitation (EP-B 0 317 378).
It has now surprisingly been found that it is possible to produce precipitated silicas in a single precipitation stage at a simultaneously elevated space-time yield and without adding electrolytes.